It is well known that accurate internal reference oscillators in satellite positioning system receivers, for example NAVSTAR GPS and Clonass receivers, reduce satellite signal acquisition times by reducing the Doppler search space. Others have therefore endeavored to provide accurate reference oscillators, especially low cost oscillators, for satellite positioning system receivers. The present inventions also provide accurate reference oscillators suitable for use in mobile wireless communication devices.
U.S. Pat. No. 5,654,718 entitled “GPS Receiver Device And Method For Calibrating A Temperature Uncompensated Crystal Oscillator”, for example, discloses the use of stored average characteristic S-curve (Beckmann) data to match reference and GPS oscillator frequencies. U.S. Pat. No. 5,654,718 also discloses storing temperature frequency offset data for subsequent GPS signal acquisition.
U.S. Pat. No. 5,841,396 entitled “GPS Receiver Utilizing A Communication Link” discloses the use of a precision carrier frequency signal from a terrestrial network to generate a reference signal for calibrating a local oscillator used by a GPS receiver to acquire GPS signals. U.S. Pat. No. 6,208,292 entitled “Position Location With Low Tolerance Oscillator” uses a scheme similar to that disclosed in U.S. Pat. No. 5,841,396 except that the oscillator correction signal is frozen when the GPS receiver makes position determinations.
U.S. Pat. No. 6,122,506 entitled “GSM Cellular Telephone And GPS Receiver Combination” discloses the use of a precision carrier frequency signal from a terrestrial network to generate a reference signal for controlling a synthesizer that provides a local oscillator signal to a GPS receiver.